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Buy a Haynes. It'll be an easy job but can't tell you for sure on the scenic.
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Bobby,
Somebody helpful who knows will be along at some point; but looking at how it comes apart is your first step. Look for a couple of pins going through the calipers and holding the pads, or it could be a single pin, but it\'ll be fairly obvious. Often they will only come out one way, so pay attention to how it appears to have been pused in. If you need to use too much hammer, then you\'re probably doing something wrong.
Your only likely point of difficulty is that your new (unworn) pads will required a bigger space than the currently worn pads.
Now you hear all sorts of things about the correct thing to do and the dangers of doing it wrong, but unless your current pads are massively worn I can\'t imagine you\'ll have too much difficulty simply pusging the cylinder back in gently, even releasing the bleed nipple if you have to move them much.
Its obviously better if you have someone with you who knows what they are doing, If not you need to be very careful and test it thoroughly afterwards, certainly before you put anyone else in the car.
Mark.
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Even if you buy a Haynes, this is not the sort of first job for a beginner.
Stick to jobs for starters that are only going to cost you money, (not other peoples lives), if you get it wrong.
I know that you have got to learn, but do it under heavily supervised conditions.
pmh (was peter)
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Aprilia,
Well said - I hope BobbyG can get it back together safely - or bring a mechanic to the car.
Matt35.
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Thanks Mark, followed your advice but discovered that it wasn't pins but bolts, a friendly neighbour saw me and helped - its actually very simple.
First wheel took me 5 hours, second 15 mins......
Thanks guys,
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Glad you got it together again, Bobby. As you mention bolts, I presume the Scenic has Girling-type calipers? For those, my Haynes manual (for Peugeots) says the bolts should be replaced with new ones, and locking compound should be used. I have never been sure whether this is essential or just desirable - did you do that?
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I think they are 'Colette' type floating calipers. Really you should replace the bolt(s) that you remove. Good quality pads usually come with replacement bolts, ready coated with 'microencapsulated' locking compound. I fit these and then carefully torque to the manufrs. spec. using my 3/8" torque wrench. Did a set only last weekend, in fact.
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Following on from Aprilia's comments ...
Micro-encapsulated locking compound is a 'use-once' retainer. The capsules comprise an anaerobic compound with a shell of activator. When the bolts are screwed in, the capsules break and the activator mixes with the compound to make it set within a few minutes.
If it is suspected that replacement bolts are coated with micro-encapsulated compound, then applying a locking compound is *essential* if the original bolts are being re-used. A liquid Loctite of the correct grade ('Nutlock' or 'Studlock', but NOT Bearing Retainer) is suitable for this. Just brush off any residue from the thread and apply the Loctite to the leading end of the thread for a length roughly equal to the bolt diameter. The Loctite won't start to harden until the bolt is screwed in.
One more point: When fitting bolts with anaerobic locking compound (whether micro-encapsulated or in liquid form), any checking of the tightening torque must be carried out within about 5 minutes, i.e. before the compound has started setting, otherwise the locking will be weak due to disturbance of the compound as it sets.
Please excuse the mini-lecture. No intention to 'talk down' to anyone, but this is a safety issue and its important to get it right!
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Interesting point here on brake pads. After years of thinking I knew how to do them, I recently found out that you should on no account just lever the pistons back in to create space for the new pads, as that sends fluid back up the pipes into the master cylinder.
Apart from the mess if it overflows, it dislodges any accumulated dirt in the caliper cylinders and pumps it into the master cylinder for general distribution. The backward flow can also damage the master cylinder seals.
The correct procedure is always to loosen the bleeder at the caliper and release surplus fluid. This way old and possibly dirty fluid is bled out of the system every time a pad is replaced.
Another DON'T is when bleeding the brakes. Never pump the pedal further down that it travels in normal use, because that runs the seals over an unfamiliar and possibly corroded section of bore, causing premature internal failure of the master cylinder. Use gentle partial strokes, or better still an Easibleed.
It was no coincidence that whenever I have had to replace a master cylinder it has been a few weeks after doing some other routine brake maintenance.
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Well said. NEVER just shove the pistons back - you can invert the seals on the m/c and possibly damage the ABS unit. Of course on some calipers (with h/brake mechanism) you need to ROTATE the pistons back into the caliper.
Open the bleed valve and gently ease/rotate the piston back.
I am not a great fan of the Easibleed; when you apply the air pressure it tends to 'aerate' the fluid a bit. I prefer to use a MityVac - draws it out by vacuum through the bleed nipple. Hand operated trigger so its dead easy to use and very controllable.
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Is this the point where I confess that I just used the same bolts that I had taken off originally? Without any solutions added? I wondered why the bolts that came off were blue at the tip and the bolts supplied with the pads were not.
Also, re the piston, I managed to just push that back with a bit of leverage! Oops!
What now?
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Well, you'll probably be OK with pushing the piston back, its not ideal but its what most people do and 90%+ get away with it. Something to thing about next time.
As regards the bolts - well its up to you, but if it were my car I'd buy some Loctite and swap them over at the next comfortable opportunity, it will only take a few minutes.
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This has been a good educative thread even for those people who have 'been there, done it and got the T shirt.'
Aprilia s comment about pressure vs vacuum bleeding has certainly made me think. Personal experience of pressure bleeding has now made me question why sometimes the brakes are softer than expected after bleeding (even when new friction material has not been used, with bedding in problems). Sometimes the system feel certainly seems to harden up after a few days, sometimes without significant use.
The question is, what happens to the air that has become dissolved in the fluid? Does it tend to collect in small bubbles that then rise to the highest points? If so, do most of these bubbles then find the way back to master cylinder reservoir or can they become trapped in the master cylinder? 'Inversions' in the pipe work would also form natural traps? Does this explain why some cars have a reputation for being difficult bleeders?
It would also suggest that bleeding with the minimum amount of fluid use is to be recomended. This would ensure fluid which will be aerated at the master cylinder fluid/air interface remains high in the system. I have always aggressively bled, since that can ensure a fluid change without specifically replacing fluid.
All in all, the original advice of 'not a beginners job' seems to become more and more relevant!
pmh (was peter)
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Ciff and Aprilia,
The theory of opening the bleed nipple when pushing the piston back is all very fine, but when I open the bleed nipple, fluid runs out by gravity even before the piston is pushed back. Presumably you have to clamp the brake hose with a "visegrip" or "mole" to stop this.
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No, just don't open it very much. Sufficient that fluid can force its way out, but not so much that it runs out.
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As I said before, I always use a vacuum bleeder and add new fluid gently - this avoids adding tiny air bubbles into the system. Pressure bleeders tend to agitate the fluid in the supply pot (when you connect the compressed air supply) and so I try not to use them.
A MityVac can be had for about £35 and they are also useful for checking vacuum components on the engine (e.g. MAP sensors etc.).
Bubbles do collect at 'points of inversion' in the brake pipes - but the narrow diameter of a brake pipe means that surface tension comes into play and so the bubble should be dragged through.
As regards pedal feel with new pads - well, due to mechanical tolerances, new pads will not be 'co-planar' with the disc surface until they have bedded in a bit, so the brakes may not be at full efficiency for a couple of hundred miles.
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